Fix UselessAssignment in ConsensusCalculator
Fix UselessAssignment in ConsensusCalculator

This was part of a since-remove debugging scheme:
```ruby
  synonyms = names.map(&:id).join(", ")
  add_debug_message("Multiple synonyms: #{synonyms}<br>")
```
See https://github.com/MushroomObserver/mushroom-observer/blame/bdd40a44e30055185abc1e55e29b63b09d85c21f/app/models/observation/consensus_calculator.rb

MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer